Steel caterpillers have usually been attached to the under-carriages of traveling construction machines, but in recent years rubber crawlers have been applied as well.
FIG. 8 shows a conventional rubber crawler 16 on which an inner flanged inner-flanged idler wheel 19 is rolling. The reference numeral 11 is a core bar. The reference numeral 12, 13 and 14 indicate a wing portion, a protruding part to prevent disengagements of a wheel, and an engaging part with a driving wheel, respectively, all of the core bar 11. The numeral 17 is a steel cord, 18 is an engaging hole, 19c is a center rolling part of the idler wheel 19. As shown in this figure, the center rolling part 19c travels between the protruding parts 13, 13 so that disengagements of the wheel can be prevented.
Compared with a steel crawler, the above rubber crawler has the disadvantage that disengagements of the crawler may easily happen. This is mainly because the rubber crawler is partially twisted to thereby disengage from the wheel, when it turns on a stepped ground in the workshop. FIG. 9 shows a disengagement of the wheel. The crawler is slided sideways between the adjacent core bars 11, 11, and therefore the center rolling part 19c of the inner-flanged idler wheel 19 runs on the protruding part 13, thereby causing the disengagement of the wheel from the crawler.
To overcome this problem, increasing the widthwise strength of the rubber crawler may be considered.
Then, if the interval of core bars in the rubber crawler is narrowed as the width thereof is broadened in order to increase the strength of the rubber crawler, the widthwise edge portions of each core bar become angulate at their turning points, which places the rubber crawler in a polygonal shape. Accordingly, the rubber crawler suffers much bending fatigue, and therefore its durability decreases.
On the other hand, if a short-pitched rubber crawler (wherein the core bars' interval is half of the conventional rubber crawlet's core bar interval by embedding core bars of narrower width arranged for the interval) is applied in order to increase the strength, it is excellent in preventing disengagements of the wheel because of the narrower interval of the embedded core bars than in a conventional rubber crawler's, and is excellent in the durability as well. However, this has not become a perfect means yet, but still causes disengagements of the crawler in a large-sized construction machine.
FIGS. 10A and 10B show the core bars 11 vibrating in a circumferential direction in the conventional rubber crawler for an inner-flanged wheel for an inner-flanged wheel. As shown in FIG, 10A, when an outer force such as a load of the wheel is imposed on the top edge portion of the protruding part 13, the core bar 11 is displaced as shown in a dotted line 13'. Accordingly, the wheel falls between the protruding parts 13 and 13 , which causes traveling vibrations of the wheel. As shown in FIG. 10B, when the protruding part 13 is pushed by an ourter force F' from the outside, the core bar 11 is displaced as shown in a dotted line 13". Such an outer force F' happens when some stones are pushed into a space between the protruding parts 13 and 13, or when chassis hook the side upper portion of the protruding part 13 due to disorders of the rubber crawler device. In this case, the core bar is pulled out at a stroke, or gradually separates from an adherent face with gum to fall off. These vibrations of the core bars are caused by the construction that each core bar receives a partial outer force nearly individually. For this solution, providing some effective connecting means between the adjacent core bars is considered.